Energy-selecting electron microscope using electron optics



United States Patent 3,256,433 ENERGY-SELECTING ELECTRON MICROSCOPE USING ELECTRON OPTICS Hiroshi Watanabe, Tokyo, and Ryozi Uyeda, Nagoya,

Japan, assignors to Hitachi, Ltd., Tokyo, Japan, a corporation of Japan Filed Mar. 26, 1963, Ser. No. 268,182 Claims priority, application Japan, Mar. 27, 1962, 37/ 11,212 9 Claims. (Cl. 250-495) The present invention relates to energy-selecting electron microscopes.

Electron beam forming an electron image in electron microscopes generally include electrons of diiferent energy values. The reason for this is that the electron beam passing through the substance under examination undergoes not only the elastic but also the inelastic scattering effect of the specimen. The electrons having obtained different energies during the passage through the specimen are incoherent to each other and, on the other hand,

of electrons passingtherethrough. Accordingly, inelastically scattered electrons sporadically reach the image plane around the image formed at points therein by elastically scattered electrons and thus deteriorate the quality of the image.

In view of the above difliculties, the present invention is intended to improve the resolving power of an electron microscope through exclusion of inelastically scattered electrons to form an image solely by elastically scattered electrons. The invention is also intended to provide a novel and unique means for excluding elastically scattered electrons, if desired, to form an electron image solely of inelastically scattered electrons, thereby enabling experimental researches to be conducted, for instance, on the scattering process of the incident electrons by the substance under examination or on the influence of inelastically scattered electrons upon the electron microscopic image.

According to the present invention, there is provided an energy-selecting electron microscope which comprises components arranged between the objective lens and the imaging plane of the microscope including first selecting means for selecting one of the electron diffraction spots on the back focal plane of the objective lens, means for energy-analyzing said electron ray selected by said first selecting means into monoenergetic electron rays, second selecting means for selecting one of said monoenergetic electron rays formed by said analyzing means, and an auxiliary lens for magnifying said monoenergetic electron ray selected by said second selecting means to form a final image on the imaging plane.

The present invention will now be described in detail with reference to the accompanying drawing, which schematically illustrates an electron microscope embodying the present invention.

Referring to the drawing, numeral 1 designates an incident electron beam emitted from an electron gun (not shown) and converged in a suitable manner. Numeral 3 designates the electron beam after passing through a specimen 2 under examination. A pattern of electron diffraction spots 5, 5', 5", is formed on the back focal plane of the objective lens 4. Numeral 6 designates a first auxiliary lens 7, a first aperture diaphragm which is movable for adjustment transverse to the longitudinal axis of the microscope; 9, an analyzing lens; 10, a second aperture diaphragm which is also movable for adjustment; and 12, a magnifying lens or second auxiliary lens. An enlarged pattern of diffraction spots 8, 8', 8", is obtained on the plane of the first aperture diaphragm, corresponding to the diffraction spots 5, 5, 5", Analyzed images the focal length of electron lenses depends upon the energy 7 values E E E are formed in the plane of the second aperture diaphragm 10 under the energy-analyzing effect of the analyzing lens 9. A final image 14 is formed on the imaging plane 13.

The incident electron beam 1 having a certain energy E is transformed during the passage through the specimen 2 into an electron beam 3, which includes electrons of different energy values E E E due to the elastic as well as inelastic scattering effects of the specimen. The electron rays forming the electron diffraction spots 5, 5, 5", on the back focal plane of the objective lens are projected through the auxiliary lens 6 to form respective magnified diffraction spots 8, 8, 8", in the plane .of the first aperture diaphragm 7, each of the electron rays forming the respective diffraction spots 8, 8', 8", also including electrons of different energy Assume, for example, that the first aperture diaphragm 7 has its aperture adjusted in position, as illustrated to allow passage therethrough only of that electron ray forming the central diffraction spot 8. The electrons forming the spot 8 will be energy-analyzed by analyzing lens 9 to form in the plane of the second aperture diaphragm 10 images 11, 11', 11", corresponding to respective different energy values E E E as a discontinuous spectrum. It is to be understood that those electrons having an energy value E are electrons elastically scattered by the specimen, all the remainder being comprised of inelastically scattered electrons.

The analyzing lens 9 as illustrated is an electrostatic unipotential lens having an extraordinarily large chromatic aberration constant, which is suitable for such energy analysis of electron beam. However, it is to be understood that the lens 9 is essentially a form of electron prism effective to disperse an electron beam in accordance with the energy difference between the electrons. It will be apparent that a pair of electron deflecting plates may also serve the purpose with success.

Each of the images formed in respective diiferent positions in the plane of the second aperture diaphragm 10 depending upon the respective energy values is thus formed by monoenergetic electrons. Under these circumstances, the aperture of the second diaphragm 10 may be adjusted in position so as to allow passage therethrough solely of those elastically scattered electrons of energy E which form the diffraction spot 11, as illustrated. The electron ray having passed through the aperture is then magnified by the magnifying lens to obtain in the imaging plane 13 a final image 14 of high resolution formed solely of elastically scattered electrons of the energy E It will readily be appreciated that by adjusting the aperture position of the second diaphragm 10, any electron ray including inelastically scattered electrons of an energy value less than E may be selected to form a monoenergetic electron image. This aflfords a means of experimentally investigating the influence of inelastically scattered electrons upon images as obtained with ordinary.

electron microscopes. Obviously, this does not preclude use of the electron microscope of the present invention in the manner conventionally employed with ordinary electron microscopes.

As apparent from the foregoing, the electron microscope of the present invention has a number of merits and a wide range of applications. First, it has an improved resolving power and enables close and accurate observations since it forms an electron image of high resolution by use of elastically scattered electrons only. Secondly, this microscope, being also capable of forming an image by use of inelastically scattered electrons only, provides an effective means of experimentally elucidating different electron-scattering processes in a specimen or the influence of inelastically scattered electrons upon electron images, which has previously been dealt with upon the basis of sheer presumptions.

What is claimed is:

1. An energy-selecting electron microscope having electron beam generating means, a specimen and an objective lens comprising components arranged between said objective lens and the imaging plane of the microscope including a first auxiliary lens, a first selecting means for selecting an electron ray forming one of the electron dilfraction spots of said specimen under examination on the back focal plane of the objective lens, means for energy-analyzing the electron ray selected by said first selecting means into monoenergetic electron rays, a second selecting means for selecting one of said monoenergetic electron rays formed by said analyzing means, and an auxiliary lens means for magnifying said monoenergetic electron ray selected by said second selecting means to form a final image on the imaging plane.

2. An energy-selecting electron microscope having electron beam generating means, a specimen and an objective lens comprising components arranged between said objective lens and the imaging plane of the microscope including a first auxiliary lens,

a first selecting means for selecting an electron ray forming one of the electron difiraction spots of said specimen under examination on the back focal plane of the objective lens,

means for separating the said electron ray into monoenergetic electron rays,

a second selecting means for selecting one of said monoenergetic electron rays formed to the exclusion of the others, and

lens means for transmitting said selected monoenergetic electron ray to the imaging plane of said electron microscope.

3. An energy-selecting electron microscope having electron beam generating means, a specimen and an objective lens comprising components arranged between said objective lens and the imaging plane of the microscope including a first auxiliary lens,

a first selecting means for selecting an electron ray forming one of the electron diffraction spots of said specimen under examination on the back focal plane of the objective lens,

means for separating the said electron ray into monoenergetic electron rays,

a second selecting means for selecting one of said monoenergetic electron rays formed to the exclusion of the others, and

- lens means for transmitting said selected monoenergetic electron ray to the imaging plane of said electron microscope,

said first and second selecting means being in the form of adjustable aperture diaphragms capable of transverse adjustment with respect to the longitudinal axis of said microscope.

4. An energy-selecting electron microscope having electron beam generating means, a specimen and an objective lens comprising components arranged between said objective lens and the imaging plane of the microscope including a first auxiliary lens,

a first selecting means for selecting an electron ray forming one of the electron diffraction spots of said specimen under examination on the back focal plane of the objective lens,

means for separating the said electron ray into monoenergetic electron rays,

a second selecting means for selecting one of said monoenergetic electron rays formed to the exclusion of the others, and

lens means for transmitting said selected monoenergetic electron ray to the imaging plane of said electron microscope,

.said means for separating the said electron ray into 4 monoenergetic electron rays being in the form of an electrostatic unipotential lens having a large chromatic aberration constant.

5. An energy-selecting electron microscope having electron beam generating means, a specimen and an objective lens comprising components arranged between said objective lens and the imaging plane of the microscope including a first auxiliary lens,

a first selecting means for selecting an electron ray forming one of the electron diffraction spots of said specimen under examination on the back focal plane of the objective lens,

means for separating the said electron ray into monoenergetic electron rays,

a second selecting means for selecting one of said monoenergetic electron rays formed to the exclusion of the others, and

said first and second selecting means being in the form of adjustable aperture diaphragms capable of transverse adjustment with respect to the longitudinal axis of said microscope,

said means for separating the said electron ray into monoenergetic electron rays being in the form of an electrostatic unipotential lens having a large chromatic aberration constant.

6. An energy-selecting electron microscope having electron beam generating means, a specimen and an objective lens comprising components arranged between said objective lens and the imaging plane of the microscope including a first auxiliary lens,

a first selecting means for selecting an electron ray forming one of the electron ditfraction spots of said specimen under examination on the back focal plane of the objective lens,

means for separating the said electron ray in-to monoenergetic electron rays,

a second selecting means for selecting one of said monoenergetic electron rays formed to the exclusion of the others, and

means for transmitting said selected monoenergetic electron ray to the imaging plane of said electron microscope,

said first and second selecting means being in the form of adjustable aperture diaphragms capable of transverse adjustment with respect to the longitudinal axis of said microscope,

said means for transmitting said selected monoenergetic electron ray to the imaging plane being in the form of a magnifying lens.

7. In an electron microscope having electron beam generating means, an objective lens, an image plane and a specimen disposed between said electron beam generating means and said objective lens, the improvement essen tially consisting of means disposed 'between said objective lens and said image plane for selectively excluding from the electron beam emanating from said specimen all electrons except those of a desired energy level comprising a first auxiliary lens,

a first selecting means for selecting an electron ray forming one of the electron difiraction spots of said specimen under examination on the back focal plane of the objective lens,

means for separating the said electron ray into monoenergetic electron rays,

a second selecting means for selecting one of said monoenergetic electron rays to the exclusion of the others, and

. auxiliary lens means for magnifying said monoenergetic electron ray selected by said second selecting means to form a final image on the imaging plane.

8. In an electron microscope having electron beam generating means, an objective lens, an image plane and a specimen disposed between said electron beam generating means and said objective lens, the improvement essentially consisting of means disposed between said objective lens and said image plane for selectively excluding from the electron beam emanating from said specimen all electrons except those of a desired energy level comprising a first auxiliary lens,

a first selecting means for selecting an electron ray forming one of the electron difiraction spots of said specimen under examination on the back focal plane of the objective lens,

means forseparating the said electron ray into monoenergetic electron rays,

a second selecting means for selecting one of said monoenergetic electron rays to the exclusion of the others, and

auxiliary lens means for magnifying said monoenergetic electron ray selected by said second selecting means to form a final image on the imaging plane,

said first and second selecting means being in the form of adjustable aperture diaphragms capable of transverse adjustment with respect to the longitudinal axis of said microscope.

9. In an electron microscope having electron beam generating means, an objective lens, an image plane and a specimen disposed between said electron beam generating means and said objective lens, the improvement essentially consisting of means disposed between said objective lens and said image plane for selectively excluding from the electron beam emanating from said specimen all electrons except those of a desired energy level comprismg a first auxiliary lens,

a first selecting means for selecting an electron ray forming one of the electron diffraction spots of said specimen under examination on the back focal plane of the objective lens,

means for separating the said electron ray into monoenergetic electron rays,

a second selecting means for selecting one of said monoenergetic electron rays to the exclusion of the others, and

auxiliary lens means for magnifying said monoenergetic electron ray selected by said second selecting means to form a final image on the imaging plane,

said means for separating the said electron ray into monoenergetic electron rays being in the form of an electrostatic unipotential lens having a large chromatic aberration constant.

References Cited by the Examiner UNITED STATES PATENTS 2,392,243 1/1946 Hillier 250-49.5 2,396,624 3/1946 Von Bor-res 250-495 2,429,558 10/1947 Marton 25049.5 X 2,494,442 1/ 1950 Le Poole 25049.5 2,894,160 7/1959 Sheldon 25049.5 3,134,899 5/1964 Guyenot et al. 250-495 FOREIGN PATENTS 760,135 11/1953 Germany.

RALPH G. NILSON, Primary Examiner.

H. S. MILLER, G. E. MATTHEWS,

Assistant Examiners. 

1. AN ENERGY-SELECTING ELECTRON MICROSCOPE HAVING ELECTRON BEAM GENERATING MEANS, A SPECIMEN AND AN OBJECTIVE LENS COMPRISING COMPONENTS ARRANGED BETWEEN SAID OBJECTIVE LENS AND THE IMAGING PLANE OF THE MICROSCOPE INCLUDING A FIRST AUXILIARY LENS, A FIRST SELECTING MEANS FOR SELECTING AN ELECTRON RAY FORMING ONE OF THE ELECTRON DIFFRACTION SPOTS OF SAID SPECIMEN UNDER EXAMINATION ON THE BACK FOCAL PLANE OF THE OBJECTIVE LENS, MEANS FOR ENERGY-ANALYZING THE ELECTRON RAY SELECTED BY SAID FIRST SELECTING MEANS INTO MONOENERGETIC ELECTRON RAYS, A SECOND SELECTING MEANS FOR SELECTING ONE OF SAID MONOENERGETIC ELECTRON RAYS FORMED BY SAID ANALYZING MEANS, AND AN AUXILIARY LENS MEANS FOR MAGNIFYING SAID MONOENERGETIC ELECTRON RAY SELECTED BY SAID SECOND SELECTING MEANS TO FORM A FINAL IMAGE ON THE IMAGING PLANE. 